Hybrid SnBi/SAC Low-Temperature Solder Bump

Assembling advanced electronic packaging at low temperature attracts attentions from the industry. One of the advantages is to reduce the warpage of dies and enhance long-term reliability of the chips. Although eutectic SnBi is considered a widely accepted low-temperature solder, Bi segregation after annealing drastically degrades the mechanical strength. In this study, two layers of materials, a pre-solder (Sn-0.3Ag-0.7 Cu, SAC0307) and a low temperature solder (Sn-56Bi-1Ag-0.2Cu, SB102) was reflowed sequentially to create a hybrid solder joint. The reflow temperatures were set as 170 and 190 oC, which are much lower than that of the SAC solder. Adding SAC0307 reduces the Bi content in the joint and lessens the formation of Bi-rich phase. Comparing with SB 102 joint, the hybrid bond shows increasing joint strength after aging. The facture surface indicates that hybrid joint exhibits ductile fracture mode while SB 102 joint shows brittle mode. The results prove that SAC0307/SB102 hybrid solder joint can be a promising candidate for low-temperature application for advanced electronic packaging.